Process principle of aluminum alloy extinction electrophoresis painting

by:Zeyi     2022-01-03
1. Process principle of aluminum alloy extinction electrophoresis painting    The extinction electrophoresis painting of aluminum alloy is carried out on the surface of the anodized film. Similar to bright electrophoresis, its production process is as follows:    degreasing → washing → alkali corrosion → washing → washing → neutralization → washing → anodizing → washing → pure water washing → electrolytic coloring → pure water washing → hot pure water washing → pure water washing → electrophoresis →RO1 water washing→RO2 water washing→drip drying→pre-drying→curing. Extinction electrophoresis and transparent electrophoresis are basically the same. Both use aluminum profiles as anodes. Under the action of direct current, an electrochemical reaction occurs. The charged paint particles move to the object to be coated under the action of electric field, so that the electrophoretic paint is deposited and deposited on the profiles. A paint film is formed on the surface, and the whole reaction includes four simultaneous processes of electrophoresis, electrolysis, electrodeposition and electroosmosis. The differences mainly include electrophoretic paint raw materials and production process parameters. The molecular weight of matte electrophoretic paint is much larger than that of bright electrophoretic paint, generally between 70,000 and 80,000 g/mol. In addition, in terms of process control, its electrophoresis voltage and tank There are differences in liquid temperature and electrophoresis time. Normally, for the same color number, the voltage, time and temperature of extinction electrophoresis are higher than those of transparent electrophoresis. In addition, compared with bright electrophoresis, there is one more pre-drying process, which reduces The water marks produced when dripping dry in cold and humid weather is closely related to the characteristics of electrophoretic paint. 2. Influencing factors and control methods for the quality of vertical oxidizing extinction electrophoresis painting. Ordinary electrophoresis painting cannot cover up the surface defects of the profile, and the extinction electrophoresis can only cover a small part of the substrate surface defects, and the oxidation production process is long and flowing. The operation has strong continuity, especially the use of oxidation vertical hanging automatic production. Often the same type of defects exist in the products produced in a period of time. The defects generated in each process stage will be basically exposed after the curing process. As a result, the yield of electrophoretic profiles is lower than that of ordinary oxidized profiles. Extinction electrophoresis is a high-end product, and the subtle defects after surface treatment are more likely to appear. The reasons and countermeasures for common defects in production are as follows:    (1) Water mark    The more consistent statement on such defects is caused by uneven water film on the surface of the profile before entering the electrophoresis tank. Especially in cold weather, the probability of occurrence is higher. We adopt to reduce hot pure water washing, extend the dripping time, or avoid the cold and humid weather and concentrate on production. For a small amount of water marks in production on hot days, one is to fully cool the profile after washing with hot water. Then enter the pure water tank before electrophoresis; then replace a certain amount of pure water in time to ensure that the temperature of the pure water tank is consistent with room temperature; third, quickly transfer the profile from the pure water tank to the electrophoresis tank, and the coordination of the operator's actions can avoid such defects appeared. In addition, ensure the stability of the electrophoresis bath.  (2) Dirt on the paint film surface   Different reasons lead to different places where the dirt gathers. If the dirt on the upper part of a row of profiles is obvious, it is generally caused by more impurity particles in the washing tank. This is because the oxide film is positively charged, while the particles in the water are negatively charged and cannot be easily removed once adsorbed. For example, the dirt on the outside of a hanging profile is generally caused by exposure of the electrophoretic profile to unclean air. When it reaches the drip-drying stage after electrophoresis, because the paint film has a certain viscosity, when there is more dust in the air, it is easy to adhere to the paint film. Of course, this type of defect can also occur when using an uncleaned curing oven or the filter screen of the curing oven is damaged. Therefore, the curing furnace needs to be cleaned regularly. After cleaning, spraying a suitable solution into the furnace can reduce the generation of furnace ash.  (3) Orange peel    is caused by uneven electrodeposition. Therefore, it is necessary to analyze the factors that accelerate the electrodeposition speed, such as bath temperature, conductivity, painting voltage, pH value, etc. These factors accelerate the migration of charged particles. Once it fluctuates to a critical value, it will increase the probability of defects. Especially when the bath temperature is greater than 25°C or the bath is contaminated by acid, the probability of such defects is higher. Therefore, the process The parameters should be kept as stable as possible. In addition, if the cleaning is not clean after oxidation, the acid in the membrane holes will flow into the electrophoresis tank, which will also cause orange peel. Therefore, the electrophoresis tank must be carefully maintained and painted in time to ensure the quality of the tank. Any irregular actions in the process are harmful to the decorative effect of the paint film. Therefore, the operation should be standardized during the unloading and packaging process, and they should be placed separately in an orderly manner.
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